TAMR is expected to be one of the future generation of magnetic recording technologies that will enable recording at ˜1-10 Tb/in2 data densities. TAMR involves raising the temperature of a small region of the magnetic medium to near its Curie temperature where both of its coercivity and anisotropy are significantly reduced and magnetic writing becomes easier to achieve even with weak write fields characteristic of small write heads in high recording density schemes. In TAMR, optical power from a light source is converted into localized heating in a recording medium during a write process to temporarily reduce the field needed to switch the magnetizations of the medium grains. Thus, with a sharp temperature gradient of TAMR acting alone or in combination with a high magnetic field gradient, data storage density can be further improved with respect to current state of the art recording technology.
In addition to the components of conventional write heads, a TAMR head also typically includes an optical wave guide (WG) and a plasmon antenna or plasmon generator (PG). The wave guide serves as an intermediate path to guide the external laser light to the PA or PG where the light optical mode couples to the local plasmon mode of the PA or to the propagating plasmon mode of the PG. After the optical energy is transformed to plasmon energy, either with local plasmon excitation in the PA or with energy transmission along the PG, it is concentrated at the medium location where heating is desired. Ideally, the heating spot is correctly aligned with the magnetic field from the write head to realize optimum TAMR performance. However, in the prior art, alignment has been difficult to achieve and the spot size is typically around 100 nm or greater which is significantly larger than the <50 nm size needed to make the first generation of TAMR devices highly efficient.
A thermally assisted magnetic head structure disclosed in U.S. Patent Application Publications 2008/0192376 and 2008/0198496 employs an edge plasmon mode that is coupled to a wave guide as represented in FIG. 1. Conventional components of a magnetic recording structure as shown as a main pole 1, return pole 3, and write coils 5 formed along an air bearing surface (ABS) 8-8. The wave guide 4 guides the input optical light wave 6 toward the ABS 8-8 in the center cross-sectional view. As shown in the prospective view, plasmon generator 2 has a triangular shape and extends a certain distance from the ABS before meeting WG 4. Optical wave 6 couples to the edge plasmon (EP) mode 7 that is excited and propagates along the sharp edge 9 of plasmon generator 2 adjacent to the WG 4. Plasmon mode 7 further delivers the optical power toward the ABS and locally heats a medium (not shown) placed underneath the plasmon generator 2. A plasmon generator is typically made of noble metals such as Ag and Au that are known to be excellent generators of optically driven surface plasmon modes. The local confinement of the edge plasmon mode 7 is determined by the angle and radius of the triangle corner.
In theory, an edge plasmon generator (EPG) can be engineered to achieve a very tiny light spot as well as a high temperature gradient in the medium for a TAMR recording scheme. Moreover, a plasmon generator with a substantial length in a direction perpendicular to the ABS will have a large metal volume that can avoid localized heating damage during TAMR writing compared to an isolated plasmon antenna of smaller volume. In TAMR, a written bit strongly depends on the thermal spot size and shape in the recording layer, and on the alignment between the magnetic gradient and thermal gradient. The magnetic medium is heated by an EPG in which the optical energy is confined around the tip of the EPG thereby forming a so-called edge plasmon mode. Clearly, the confinement of the optical spot or EP mode in this design is a function of the shape, angle, and size of the tip, the metal composition of the EPG, and the dielectric material surrounding the tip.
Referring to FIG. 2a, optical modeling data for a 90 degree gold EPG is shown that indicates the dependency of optical spot size in a cross-track direction on the tip radius of the EPG. It should be understood that although the design typically includes a “V” shape for the tip, the actual shape realized from state of the art fabrication methods is substantially rounded as illustrated in FIG. 2b with a tip radius r. For a 25 nm tip radius, the optical spot size in the medium is about 100 nm (FIG. 2a). Even with a 5 nm tip radius, it is difficult to obtain a spot size less than 50 nm which is desired for the first generation of TAMR products. Furthermore, those skilled in the art will appreciate that it is very difficult to fabricate a sharp tip with a 5 nm tip radius with good tolerance necessary for a manufacturing process.
Thus, there is a need to further reduce spot size using an EPG tip radius that is easily manufactured in order to improve the performance of TAMR writing and make it competitive with other new technologies such as microwave assisted magnetic recording (MAMR).
A routine search of the prior art resulted in the following references. However, there is still an unmet need to reduce heating spot size in a TAMR design.
U.S. Pat. No. 7,643,248 discloses a plasmon resonator having a metal pin where the oscillation direction of the surface plasmon of a conductive body is about parallel to the oscillation direction of the surface plasmon of a conductive scatterer.
In U.S. Pat. No. 7,612,323, an optical element is described that generates near-field light smaller than a condensing spot near a condensing point.
U.S. Pat. No. 7,596,072 teaches that optical spot dimensions are determined by the dimensions of a small metal structure inside an optical recording head that includes a waveguide and phase change storage medium. Theoretically, the optical spot can be as small as 20 nm.
In U.S. Pat. No. 7,547,868, an optical near-field generating apparatus includes a conductive scatterer that causes an optical near field based on a surface plasmon to be generated by being illuminated by incident light. A small optical spot can be achieved.
In U.S. Patent Application 2003/0011722, a light shielding film in a near-field light generating element is disclosed.